The long-term goals of this project are to gain insights into the mechanisms by which BMP3 regulates osteogenesis. Although research on bone morphogenetic proteins (BMPs) has expanded exponentially over the past decade, we actually know very little about the physiological roles that individual BMPs have in the skeleton. Our decision to focus this proposal on BMP3 is based on several important findings. First, although BMP3 is the most abundant BMP in bone, accounting for over 65% of the total BMP stored in bone matrix, little is known about its biology. A second reason for our interest in BMP3 are recent reports that correlate changes in BMP3 levels in vivo with fracture healing, mechanical loading of the skeleton, and the loss of bone formation that occurs with aging. Finally, and perhaps most intriguing, is our observation that BMP3 null mice display a high bone mass phenotype that increases with advancing age. In vitro, BMP3 is able to exert an inhibitor effect on osteoblast differentiation in the presence of potent osteogenic stimuli. These findings suggest that BMP3 is a negative regulator of bone mass. As osteogenic BMPs are now therapeutic agents used to augment bone formation in thousands of patients each year, understanding how BMP3 exerts its negative effect on bone mass has wide-ranging clinical significance. In this proposal, we focus on identifying the cis-regulatory elements that target BMP3 expression to bone in vivo, and determining if separable perichondrial, periosteal and osteoblast-specific enhancers that regulate BMP3 expression can be identified using a BMP3 BAC cloning strategy. PUBLIC HEALTH RELEVANCE: Musculoskeletal diseases present a major economic burden to the healthcare system, and negatively affect the quality of life of people of all ages and economic resources. Research outlined in this proposal examines the mechanism by which BMP3 exerts a negative effect on bone formation and on mesenchymal stem cell differentiation. A better understanding of the influences of BMP3 on the skeleton will allow for the development of novel treatments for musculoskeletal disorders.